Positive relationship between activity in a novel environment and operant ethanol self-administration in rats

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Abstract

Rationale. The study of individual differences in drug addiction may have important implications both for understanding the etiology of addiction and for strategies for treatment. Activity of rodents in novel environments, presumably related to the novelty-seeking trait in humans, is the primary behavioral feature that is hypothesized to predict a predisposition for drug self-administration by rodents.

Objectives. The aim of this study was to characterize the relationship between motor activity in a novel environment and operant ethanol self-administration using the sucrose-substitution procedure.

Methods. Male Long-Evans rats were exposed to a novel environment for 2 h, and the distance traversed, rearing, and defecation was recorded. After 3 days of forced exposure to ethanol the sucrose-substitution procedure began and lasted for 23 days. Following sucrose substitution the animals were maintained on a schedule of ethanol (10% v/v) self-administration with a fixed ratio 3 (FR3) for 15 days.

Results. The activity (distance traversed) in the novel environment was positively correlated with initial ethanol self-administration under the FR3 schedule (r=0.87) but not with the number of inactive lever presses or active lever presses for ethanol or for sweetened ethanol solutions with lower ratios of response. In contrast, rearing was correlated positively only with the number of inactive lever presses for sucrose.

Conclusions. Motor activity in a novel environment may be related to the acquisition of operant ethanol self-administration only when a given ratio of response is required.